Patch "net: nsh: Use correct mac_offset to unwind gso skb in nsh_gso_segment()" has been added to the 4.19-stable tree

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This is a note to let you know that I've just added the patch titled

    net: nsh: Use correct mac_offset to unwind gso skb in nsh_gso_segment()

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-nsh-use-correct-mac_offset-to-unwind-gso-skb-in-.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ef0f225a206707f33dc84bbeca5ab74ccb5e68ab
Author: Dong Chenchen <dongchenchen2@xxxxxxxxxx>
Date:   Thu May 11 20:54:40 2023 +0800

    net: nsh: Use correct mac_offset to unwind gso skb in nsh_gso_segment()
    
    [ Upstream commit c83b49383b595be50647f0c764a48c78b5f3c4f8 ]
    
    As the call trace shows, skb_panic was caused by wrong skb->mac_header
    in nsh_gso_segment():
    
    invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
    CPU: 3 PID: 2737 Comm: syz Not tainted 6.3.0-next-20230505 #1
    RIP: 0010:skb_panic+0xda/0xe0
    call Trace:
     skb_push+0x91/0xa0
     nsh_gso_segment+0x4f3/0x570
     skb_mac_gso_segment+0x19e/0x270
     __skb_gso_segment+0x1e8/0x3c0
     validate_xmit_skb+0x452/0x890
     validate_xmit_skb_list+0x99/0xd0
     sch_direct_xmit+0x294/0x7c0
     __dev_queue_xmit+0x16f0/0x1d70
     packet_xmit+0x185/0x210
     packet_snd+0xc15/0x1170
     packet_sendmsg+0x7b/0xa0
     sock_sendmsg+0x14f/0x160
    
    The root cause is:
    nsh_gso_segment() use skb->network_header - nhoff to reset mac_header
    in skb_gso_error_unwind() if inner-layer protocol gso fails.
    However, skb->network_header may be reset by inner-layer protocol
    gso function e.g. mpls_gso_segment. skb->mac_header reset by the
    inaccurate network_header will be larger than skb headroom.
    
    nsh_gso_segment
        nhoff = skb->network_header - skb->mac_header;
        __skb_pull(skb,nsh_len)
        skb_mac_gso_segment
            mpls_gso_segment
                skb_reset_network_header(skb);//skb->network_header+=nsh_len
                return -EINVAL;
        skb_gso_error_unwind
            skb_push(skb, nsh_len);
            skb->mac_header = skb->network_header - nhoff;
            // skb->mac_header > skb->headroom, cause skb_push panic
    
    Use correct mac_offset to restore mac_header and get rid of nhoff.
    
    Fixes: c411ed854584 ("nsh: add GSO support")
    Reported-by: syzbot+632b5d9964208bfef8c0@xxxxxxxxxxxxxxxxxxxxxxxxx
    Suggested-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Signed-off-by: Dong Chenchen <dongchenchen2@xxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/nsh/nsh.c b/net/nsh/nsh.c
index 1a30e165eeb4f..a5fa25555d7eb 100644
--- a/net/nsh/nsh.c
+++ b/net/nsh/nsh.c
@@ -80,13 +80,12 @@ static struct sk_buff *nsh_gso_segment(struct sk_buff *skb,
 				       netdev_features_t features)
 {
 	struct sk_buff *segs = ERR_PTR(-EINVAL);
+	u16 mac_offset = skb->mac_header;
 	unsigned int nsh_len, mac_len;
 	__be16 proto;
-	int nhoff;
 
 	skb_reset_network_header(skb);
 
-	nhoff = skb->network_header - skb->mac_header;
 	mac_len = skb->mac_len;
 
 	if (unlikely(!pskb_may_pull(skb, NSH_BASE_HDR_LEN)))
@@ -111,15 +110,14 @@ static struct sk_buff *nsh_gso_segment(struct sk_buff *skb,
 	segs = skb_mac_gso_segment(skb, features);
 	if (IS_ERR_OR_NULL(segs)) {
 		skb_gso_error_unwind(skb, htons(ETH_P_NSH), nsh_len,
-				     skb->network_header - nhoff,
-				     mac_len);
+				     mac_offset, mac_len);
 		goto out;
 	}
 
 	for (skb = segs; skb; skb = skb->next) {
 		skb->protocol = htons(ETH_P_NSH);
 		__skb_push(skb, nsh_len);
-		skb_set_mac_header(skb, -nhoff);
+		skb->mac_header = mac_offset;
 		skb->network_header = skb->mac_header + mac_len;
 		skb->mac_len = mac_len;
 	}



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